1. Field of the Invention
The present invention generally relates to illuminating devices and, more specifically, to light pipes and light guides. The assembly according to the present invention will find utility in vehicle lighting systems, as well as in a variety of non-automotive illumination applications.
2. Description of Related Art
Light pipes and light guides are used in exterior vehicle lighting applications and a variety of other applications, such as interior vehicle lighting applications, interior and exterior architectural lighting, and backlighting for liquid crystal display screens. A typical light pipe has an elongate shape and light-emitting diodes (LEDs) at both ends of the light pipe. Generally, a plurality of prisms or prismatic cuts are formed within the light pipe, which are intended to reflect light out of a side of the light pipe. The prismatic cuts are disposed on one face of the light pipe and a light-emitting face is disposed opposite the prismatic cuts. Light rays entering an end (or both ends) of the light pipe are incident at the surface of the prismatic cuts, and are reflected back through the cross-section of the light pipe so as to exit the light pipe through the light-emitting face, which is disposed opposite the face having the prismatic cuts, as noted above.
Light pipes can be oriented vertically or horizontally. The prismatic cuts are typically designed with large angles of inclusion, so that when a light beam traveling within the light pipe hits a particular prism or prismatic cut, the light beam is totally internally reflected and exits the light pipe through the surface opposite the prismatic cut. However, when a light pipe is tilted away from an axis perpendicular to the line of sight, light is reflected out of the light pipe at an oblique angle to the line of sight. In such a situation, the light pipe appears to emit less light and appears dimmer than if the light pipe was oriented perpendicular to the line of sight.
In the context of vehicle exterior lighting, exterior lights must emit enough light to meet governmental photometric requirements. Additionally, styling desires require light pipes to be oriented around curves to have rake and plan angles that are not perpendicular to the line of sight. As the styling requirements are achieved, the governmental photometric requirements become difficult to achieve, and vice versa. Some of the problems of light control have been addressed by placing light sources at both ends of the light pipe, because a single light source at one end of a light pipe has not typically been capable of providing light to a distal end of a light pipe having curves, rake, and plan angles that are not perpendicular to the line of sight. However, using only one light source would be more advantageous in the context of packaging requirements, thermal performance, and cost.
In view of the above, it is apparent that there exists a need for a light pipe that can be tilted at an angle from the line of sight and/or oriented around curves and still continue to meet governmental and vehicle manufacturer photometric requirements for light emission.